The present invention relates to molded articles and methods for manufacturing such articles. More particularly this invention is directed to injection molded articles formed from a blend of a polybenzimidazole and a polyaryleneketone.
Polybenzimidazoles are polymers of high thermal stability and are resistant to oxidative or hydrolytic degradation. Polybenzimidazole polymers may be prepared by melt polymerizing an aromatic tetraamine and a diphenylester or an anhydride of an aromatic or heterocyclic dicarboxylic acid in a one or two-stage process; see, for example H. Vogle and C. S. Marvel, Journal of Polymer Science, Col. Vol. L, pp. 511-539 (1961); and U.S. Pat. Nos. 26,065; 3,174,947; 3,509,108; 3,551,389; 3,433,772; and 3,655,632. In particular, U.S. Pat. No. 3,551,389 discloses a two-stage process for the production of aromatic polybenzimidazoles, in which the monomers are heated at a temperature above 170.degree. C. in a first-stage melt polymerization zone until a foamed prepolymer is formed. The foamed prepolymer is cooled, pulverized, and introduced into a second stage polymerization zone where it is heated again to yield a polybenzimidazole polymer product. Polybenzimidazoles also may be prepared from the free dicarboxylic acids or the methyl esters of such acids.
It is, however, difficult to mold articles from polybenzimidazole resins, and in fact, there are no known techniques with respect to injection molding polybenzimidazole or blends thereof. Compression molding of polybenzimidazole high polymers is known and is described in U.S. Pat. No. 3,340,325. As described therein, a prepolymer was prepared by reacting a diphenylester of an aromatic dicarboxylic acid and an aromatic tetraamine to a degree short of substantial infusibility. The prepolymer is fusible at temperatures in the range of from about 200.degree. F. to about 500.degree. F. A mixture of the polybenzimidazole prepolymer and polybenzimidazole high polymer was introduced into a mold, sufficient heat and pressure was applied to cause the prepolymer to become fluid and the mixture was maintained under this heat and pressure to sufficiently cure the prepolymer.
Compression molding of polybenzimidazole high polymer has been reported by Jones et al (International Conference on Composite Materials IV, AIME, Warrendale, Pa., p. 1591). Polybenzimidazole was compression molded at a temperature of 600.degree.-800.degree. F. at a pressure of 2000 psi and a final hold time of over one hour. However, employing the described process permits only one part to be made per mold per cycle, with total cycle times limited to one per normal eight-hour shift and part thickness was effectively limited to less than one inch.
It is also known to utilize matched metal die compression molding of the polybenzimidazole at temperatures of up to 875.degree. F., pressures of 5,000 to 10,000 psi and cycle times of 4-8 hours to result in molded polybenzimidazole parts. These parts are, however, limited to a quarter inch in thickness with tensile strengths up to 21,000 psi. These molded articles typically exhibit significant blistering and dimensional distortion when exposed to temperatures of 900.F for as little as five minutes.
The manufacture of sintered polybenzimidazole articles is disclosed in U.S. Pat. No. 4,814,530. As described therein, a dried particulate polybenzimidazole resin is compacted under a pressure of 2,000 to 10,000 psi in a mold, heated to a temperature in the range of 825.degree. to 925.degree. F., cooled to a temperature below 800.degree. F. and subsequently postcured.
These various techniques for molding polybenzimidazole, however, typically require the use of high temperature and high pressure, thereby reducing the processability of the polybenzimidazole and limiting the applications thereof. Moreover, there are no known techniques prior to the present invention with respect to injection molding polybenzimidazole or blends thereof.
With respect to molding polyaryleneketones, various molding techniques, such as sinter molding, injection molding and compression molding are known in the art. However, molded articles of polyaryleneketone have limited thermal and pressure resistance compared to polybenzimidazoles and thus also have limited utility